AN UNDESCRIBED AUSTRALIAN OYSTIPHYLLID ETHERIDGE. 19 



in our present fossil — a longitudinal cavity without mural invest- 

 ment enveloped in cyst-like tissue. The latter genus, Meso- 

 phyllum, Schliiter ( = Spongophylloides, Meyer), is but an ampli- 

 fication of Actinocystis, by increase of the septal area, correspond- 

 ing decrease of the vesicular peripheral zone, and a modified 

 pinnate arrangement of the septal lamelhe ; as in the former, 

 tabulae are said to be absent. To sum up, my conception of this 

 coral is that of a loosely constructed compound Actinocystis with 

 tabulae. 



Were the question put to me, how does Mictocyslis differ from 

 Endophyllum, as we understand the latter, I would answer, it 

 is possibly very much a matter of degree, although there is more 

 than one marked feature that will serve to distinguish them, 

 thus — In Endophyllum the corallites are formed by a series of 

 invaginated ob-cones, the free calicinal edges of which lie over 

 and connect with those of contiguous corallites. To a certain 

 extent, therefore, they possess a kind of spurious mural invest- 

 ment, whilst in Mictocystis, as I have already explained, even 

 that does not exist. Again, in Endophyllum the vesicular tissue 

 lies between more or less horizontal laminae, the extensions of 

 these invaginated cup-edges, instead of forming a mass of 

 heaped-up cysts. Further, the septa at their distal or outer ends 

 mingle, or are lost in the vesicular tissue, but in Mictocystis they 

 seem to be absolutely free of any connection with the vesicular 

 tissue. In fact the septal lamellae and tabulae of Mictocystis 

 resemble a series of long plugs dropped into cylindrical holes in 

 the tissue. 



Dr. C. Rominger desci'ibed a compound vesicular genus from 

 the Niagara Group of Michigan, called Vesiczdaria, 1 composed of 

 a "superimposed series of calycinal cups, of coarsely blistered 

 surface, which in vertical sections appear as a uniform succession 

 of layers of large, unequal, vesiculose plates, perfectly resembling 

 a vertical section through a Cystiphyllum." The blistered caly- 

 cinal layers bear pseudo-costal radii, and the margins of the 

 calyces are expanded and confluent without lines of demarcation. 

 At a casual glance there is some resemblance to Mictocystis, 

 principally in consequence of the blistered surface, but the 

 invaginated form of the calyces and the lateral extension of the 

 pseudo-costae at once distinguish the corals from one another. 

 Furthermore, the name Vesicularia, Rom., does not stand, having 

 been used as a genus of Polyzoa by Dr. J, V. Thompson between 

 the years 1829-1834. 



1 Vesicularia, Rominger, 1S76 (non Thompson, 1S29-34), Geol. Survey 

 Michigan. Report Lower Peninsula, 1873-76, iii., 1S7G, pt. 2, p. 135. 



